This invention relates to a manufacturing method for an MIS-type semiconductor device.
In an MIS-type semiconductor device, it is necessary to make the distances between gate and source as well as between gate and drain as small as possible to improve its characteristics. FIG. 1 shows a sectional view illustrating an MIS semiconductor device fabricated by a conventional method wherein the reference numeral 1 designates an N-type silicon substrate, 2 a P-type source region, 3 a P-type drain region, 4 an oxide layer, 5 a source electrode, 6 a gate electrode and 7 a drain electrode, respectively. Such an MIS-type semiconductor device is made by photoresist etching of a substrate material using a mask on which a pattern of source and drain is previously drawn, and next re-etching with another mask on which a gate pattern is drawn. There is a problem, however, in that the distances between the gate and the source as well as between the gate and the drain are not always same due to registry errors which may happen upon putting the masks on the substrate, thereby causing variability of the characteristics of the devices. Further, since enough space must be reserved to accommodate this error, the actual effective area decreases with respect to the total necessary device fabrication area.
FIG. 2 illustrates an MIS-type semiconductor device fabricated by another method in order to eliminate the above-mentioned drawbacks, where the source, gate and drain are formed by using one mask in a self-alignment manner. With this method, since each region is formed in self-alignment, the registry error problem between these two masking steps is eliminated. However, the distances between the gate and the source as well as between the gate and the drain are small, thus causing the drawback that the capacity between the gate and the source as well as the gate and the drain is increased undesirably. In particular, overlap of the gate and drain regions must be avoided if device speed is to be maximized. Alternatively, when using a metallic material like molybdenum to form electrode structures, it is necessary to form the regions of the source and the drain by an ion implantation method, thus raising the production cost. Moreover, both of the foregoing methods as shown leave the high-field regions of the gate electrode 6 unprotected from surface contaminants, giving rise to drift instability from ion migration.